1. Field of the Invention
This invention relates to room temperature vulcanizable (RTV) organopolysiloxane compositions which are readily vulcanizable with moisture in the air to form rubbery elastomers and more particularly, to such RTV compositions which are vulcanizable into rubbery elastomers having improved water immersion-resistant and thermoresistant adhesion to substrates which are otherwise difficult to bond.
2. Prior Art
Of prior art room temperature vulcanizable (RTV) organopolysiloxane compositions, one-part RTV silicone compositions are well known. These compositions are stored in the absence of moisture. When it is desired to cure the composition, the package is opened and the composition is applied to any desired site whereupon it reacts with moisture in the air and cures into a rubbery elastomer.
Early RTV organopolysiloxane compositions were comprised of a silanol-terminated polymer, an acyloxy crosslinking agent and a tin catalyst. Alkoxy functional type compositions were then developed. More illustratively, Nitzsche and Wick U.S. Pat. No. 3,065,194 discloses a silicone rubber composition comprising a diorganopolysiloxane having a silanol end-blocking group, an alkoxy functional cross-linking agent, and a metal salt of a chelate organometallic compound serving as a crosslinking catalyst. Other one-part alkoxy functional RTV compositions include a composition of a silanol end-blocked diorganopolysiloxane premixed with a crosslinking catalyst as disclosed in Brown et al. U.S. Pat. No. 3,161,614 and a composition comprising an alkoxy end-blocked linear siloxane polymer and a solid catalyst as disclosed in Cooper et al. U.S. Pat. No. 3,383,355. Furthermore, U.S. Pat. No. 3,499,859 discloses a hydrocarboxy end-blocked diorganopolysiloxane polymer and a metal-containing curing catalyst used in combination with boron nitride. Cooper et al., U.S. Pat. No. 3,542,901 discloses a composition comprising a mixture of a linear siloxane having di- or tri-functional end-blocking units and a linear siloxane having a chemically non-functional inert end-blocking unit at one end and a di- or tri-functional end-blocking unit at another end, a catalyst, and a crosslinking agent. Brown et al. U.S. Pat. No. 3,122,522 discloses an organopolysiloxane intermediate containing cellosolvoxyl blendable with a catalyst. Weyenberg U.S. Pat. No. 3,175,993 discloses an organopolysiloxane intermediate end blocked with an alkoxylated silcarbane group together with a catalyst.
However, the aforementioned catalysts are disadvantageous in these alkoxy systems, and the titanium salts disclosed are likely to gel and give rise to an undesirable viscosity increase during mixing and long-term storage prior to use.
As solutions to these problems, Smith and Hamilton U.S. Pat. No. 3,689,454 and 3,779,986, Weyenberg U.S. Pat. No. 3,294,739 and 3,334,067, and Clark et al. U.S. Pat. No. 3,719,635 disclose alkoxy-curable compositions utilizing titanium ester chelate catalysts instead of the metal salts of the aforementioned patents. The titanium chelate catalysts serve to control gelation and control an undesirable viscosity increase during mixing and storage for a long term of 1 or 2 years. More specifically, in conjunction with the one-part type alkoxy RTV composition, Weyenberg U.S. Pat. No. 3,294,739 and 3,334,067 disclose titanium chelate catalysts which are advantageously used to prepare appropriate curable compositions.
These prior art RTV organopolysiloxane compositions, however, have problems in adhesion to aluminum stocks which have been surface treated for good weatherability. When the RTV compositions are applied to such aluminum stocks, long-term heating and water immersion can result in peeling. Without primers, these compositions do not bond well to difficult-to-bond substrates which have recently enjoyed a widespread use, for example, fluoro-resin coated steel strips and acrylic resin electrodeposited steel strips. Additionally thermoresistant and water immersion-resistant adhesion is unsatisfactory. An improvement in these problems is thus desired.